The field of the invention comprises printing apparatus and more particularly is concerned with printing apparatus which operates on electrostatic principles rather than upon the conventional principles of graphic art printing as known today.
Color printing is effected today by mixing the colors on the final receptor through the use of multiple registered impressions. For example, a color object or image is photographed through several filters to make color separations in the printed colors comprising cyan, magenta, yellow and black. These separations are made into plates which are mounted in a printing press and the substrate such as paper is passed through the press and impressed with each of the plates in turn.
Various attempts to use electrostatic techniques for multicolor printing are known but for the most part these are complex, expensive and unreliable. The separation of the original master into plates of different basic colors is still normally required and the process contemplates the use of xerography or electrofax techniques for multiple printing.
The invention differs from the prior art in that the images to be printed are formed by electrostatic techniques semipermanently on sleeves that remain so imaged throughout the entire printing run, while in the prior art which uses electrostatic techniques there is a direct transfer or imaging for each example printed.
The invention also differs from other printing presses in that there is a separate station for each color to be printed so that different parameters which may be required for each color may be achieved at the respective stations without interfering with the imprinting of the colors from other stations.